Electric vehicle and energy storage power station usually need power battery having large capacity as the power source. Except large capacity, the power battery should also perform better safety and have a longer cycle life, so as to meet application standards and satisfy people's requirements.
In the prior art, when a power battery is over charged, decomposition of electrolyte in power battery will generate excessive heat in the interior of the power battery, which may cause burning of the battery, or increase the internal pressure of the power battery, leading to explosion of the battery (as long as the power battery is not stopped being charged, the internal pressure will increase continuously, until explosion occurs). Therefore, before the power battery is out of control, an external short circuit structure is needed to cut off the connecting component between a positive electrode tab and a positive electrode terminal (or between a negative electrode tab and a negative electrode terminal), so as to stop charging the power battery continuously. Generally, in order to solve abuse nailing problem of the battery, a resistance is arranged between a positive electrode terminal and a top cover plate, so that the positive electrode terminal is electrically connected with the top cover plate through the resistance.
When a power battery is in a situation of being nailed, if the resistance between the positive electrode terminal and the top cover plate is too small, then the current of external short circuit is too large when nailing, the nailing point is easy to spark, causing the cell be out of control, therefore, when nailing, a large resistance is needed between the positive electrode terminal and the top cover plate.
When a power battery is over charged, the internal pressure of the cell increases for a certain value, the short circuit component deforms upward, so that the positive electrode and the negative electrode of the cell are connected to form a short circuit, a large loop current is used to fuse the connecting component, so as to cut off the main loop. However, if the positive electrode and the negative electrode are connected to form a short circuit, since the resistance in the loop is so small that the current in the loop will be too large (such as, exceeding 10000 A), the short circuit component is easy to be fused, thus the short circuit component is fused before the connecting component is fused, which leads to that the loop current cannot maintain, then the connecting component cannot be fused; but if the resistance in the loop is too large, which will cause that the current in the loop is too small (such as, less than 500 A), the connecting component will not be fused, which cannot prevent the power battery from being charged continuously. Therefore, when dealing with over-charging of the power battery; it is obvious that the manner of directly connecting a large resistance is not applicable to reduce current.
Based on the above-mentioned reasons, in order to satisfy the over-charging and nailing problems of the power battery at the same time, the top cover structure of the power battery is needed to be re-optimized, so that the power battery can constitute a loop having an appropriate resistance value under the situations of over-charging and nailing.